[AST] Delete broken, unused template.

[ymandel]

Summary

The const* overload of IgnoreExprNodes can't compile. Moreover, this didn't
turn up because it's unused. There's no obvious fix, so I've deleted it.

[ymandel]

Fixed in another commit.

clang/include/clang/AST/IgnoreExpr.h

template <typename... FnTys> Expr *IgnoreExprNodes(Expr *E, FnTys &&... Fns) {
   Expr *LastE = nullptr;
   while (E != LastE) {
     LastE = E;
     E = detail::IgnoreExprNodesImpl(E, std::forward<FnTys>(Fns)...);
   }
   return E;
 }
 
-template <typename... FnTys>
-const Expr *IgnoreExprNodes(const Expr *E, FnTys &&...Fns) {
-  return const_cast<Expr *>(IgnoreExprNodes(E, std::forward<FnTys>(Fns)...));
-}
-
 inline Expr *IgnoreImplicitCastsSingleStep(Expr *E) {
   if (auto *ICE = dyn_cast<ImplicitCastExpr>(E))
     return ICE->getSubExpr();
 
   if (auto *FE = dyn_cast<FullExpr>(E))
     return FE->getSubExpr();
 
   return E;